Don't use ls | grep. Use a glob or a for loop with a condition to allow non-alphanumeric filenames.

Problematic code:

ls /directory | grep mystring

or

rm $(ls | grep -v '\.c$')

Correct code:

ls /directory/*mystring*

or

# BASH
shopt -s extglob
rm -- !(*.c)

# POSIX
for f in ./*
do
  case $f in
    *.c) true;;
    *) rm "$f";;
  esac
done

Rationale:

Parsing ls is generally a bad idea because the output is fragile and human readable. To better handle non-alphanumeric filenames, use a glob. If you need more advanced matching than a glob can provide, use a for loop.

Exceptions:

• ls has sorting options that are tricky to get right with other commands. If a specific order of files is needed, ls <sort options> | grep might be the best alternative.
• network shares like AFS behave much faster using ls

Related resources:

• BashFaq: How can I find and safely handle file names containing newlines, spaces or both?